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Index: sys/compat/linux/linux_mmap.c
===================================================================
--- sys/compat/linux/linux_mmap.c
+++ sys/compat/linux/linux_mmap.c
@@ -38,9 +38,11 @@
#include <sys/file.h>
#include <sys/imgact.h>
#include <sys/ktr.h>
+#include <sys/lock.h>
#include <sys/mman.h>
#include <sys/proc.h>
#include <sys/resourcevar.h>
+#include <sys/rwlock.h>
#include <sys/syscallsubr.h>
#include <sys/sysent.h>
#include <sys/sysproto.h>
@@ -48,6 +50,7 @@
#include <vm/pmap.h>
#include <vm/vm_extern.h>
#include <vm/vm_map.h>
+#include <vm/vm_object.h>
#include <compat/linux/linux_emul.h>
#include <compat/linux/linux_mib.h>
@@ -242,6 +245,98 @@
return (kern_mprotect(td, addr, len, prot));
}
+/*
+ * Implement Linux madvise(MADV_DONTNEED), which has unusual semantics: for
+ * anonymous memory, pages in the range are immediately discarded.
+ */
+static int
+linux_madvise_dontneed(struct thread *td, vm_offset_t start, vm_offset_t end)
+{
+ vm_map_t map;
+ vm_map_entry_t entry;
+ vm_object_t backing_object, object;
+ vm_offset_t estart, eend;
+ vm_pindex_t pstart, pend;
+ int error;
+
+ map = &td->td_proc->p_vmspace->vm_map;
+
+ if (!vm_map_check_range(map, start, end))
+ return (EINVAL);
+ start = trunc_page(start);
+ end = round_page(end);
+
+ error = 0;
+ vm_map_lock_read(map);
+ if (!vm_map_lookup_entry(map, start, &entry))
+ entry = vm_map_entry_succ(entry);
+ for (; entry->start < end; entry = vm_map_entry_succ(entry)) {
+ if ((entry->eflags & MAP_ENTRY_IS_SUB_MAP) != 0)
+ continue;
+
+ if (entry->wired_count != 0) {
+ error = EINVAL;
+ break;
+ }
+
+ object = entry->object.vm_object;
+ if (object == NULL)
+ continue;
+
+ pstart = OFF_TO_IDX(entry->offset);
+ if (start > entry->start) {
+ pstart += atop(start - entry->start);
+ estart = start;
+ } else {
+ estart = entry->start;
+ }
+ pend = OFF_TO_IDX(entry->offset) +
+ atop(entry->end - entry->start);
+ if (entry->end > end) {
+ pend -= atop(entry->end - end);
+ eend = end;
+ } else {
+ eend = entry->end;
+ }
+
+ if ((object->flags & (OBJ_ANON | OBJ_ONEMAPPING)) ==
+ (OBJ_ANON | OBJ_ONEMAPPING)) {
+ /*
+ * Singly-mapped anonymous memory is discarded. This
+ * does not match Linux's semantics when the object
+ * belongs to a shadow chain of length > 1, since
+ * subsequent faults may retrieve pages from an
+ * intermediate anonymous object. However, handling
+ * this case correctly introduces a fair bit of
+ * complexity.
+ */
+ VM_OBJECT_WLOCK(object);
+ if ((object->flags & OBJ_ONEMAPPING) != 0) {
+ vm_object_collapse(object);
+ vm_object_page_remove(object, pstart, pend, 0);
+ backing_object = object->backing_object;
+ if (backing_object != NULL &&
+ (backing_object->flags & OBJ_ANON) != 0)
+ linux_msg(td,
+ "possibly incorrect MADV_DONTNEED");
+ VM_OBJECT_WUNLOCK(object);
+ continue;
+ }
+ VM_OBJECT_WUNLOCK(object);
+ }
+
+ /*
+ * Handle shared mappings. Remove them outright instead of
+ * calling pmap_advise(), for consistency with Linux.
+ */
+ pmap_remove(map->pmap, estart, eend);
+ vm_object_madvise(object, pstart, pend, MADV_DONTNEED);
+ }
+ vm_map_unlock_read(map);
+
+ return (error);
+}
+
int
linux_madvise_common(struct thread *td, uintptr_t addr, size_t len, int l_behav)
{
@@ -261,12 +356,7 @@
behav = MADV_WILLNEED;
break;
case LINUX_MADV_DONTNEED:
- /*
- * Note that the semantics of Linux MADV_DONTNEED is very
- * different from the FreeBSD's madvise(2) flag of the same name.
- */
- behav = MADV_DONTNEED;
- break;
+ return (linux_madvise_dontneed(td, addr, addr + len));
case LINUX_MADV_FREE:
behav = MADV_FREE;
break;

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